Systemic primary carnitine deficiency

Systemic primary carnitine deficiency (SPCD), also known as carnitine uptake defect, carnitine transporter deficiency, or OCTN2 deficiency, is a rare inherited disorder of fatty acid oxidation caused by mutations in the SLC22A5 gene, which encodes the high-affinity carnitine transporter OCTN2. This transporter is responsible for the active uptake of carnitine into cells and its reabsorption in the kidneys. Without functional OCTN2, carnitine is lost in the urine, leading to severely depleted carnitine levels in blood and tissues. Carnitine is essential for transporting long-chain fatty acids into mitochondria for energy production, particularly during periods of fasting or metabolic stress. The disease primarily affects the heart, skeletal muscles, and liver. Clinical presentation is variable and can occur in two main forms. The metabolic presentation typically appears in infancy or early childhood (between ages 1 and 7 years) with hypoketotic hypoglycemia, hepatomegaly, elevated liver transaminases, and hyperammonemia, often triggered by fasting or intercurrent illness. The cardiac presentation usually manifests later, often between ages 2 and 4, with progressive dilated cardiomyopathy and heart failure, skeletal muscle weakness, and fatigue. Some individuals, particularly mothers identified through newborn screening of their affected infants, may remain asymptomatic or present with only mild fatigue into adulthood, though they remain at risk for sudden cardiac events. Treatment with oral L-carnitine supplementation is highly effective and considered lifelong. Carnitine replacement corrects the metabolic abnormalities, reverses cardiomyopathy in most cases, and prevents further episodes of metabolic decompensation. Early diagnosis, increasingly achieved through newborn screening programs that detect low free carnitine levels on dried blood spots, has significantly improved outcomes. Avoidance of prolonged fasting is also recommended. With consistent treatment, the prognosis is generally excellent, though discontinuation of carnitine supplementation can lead to life-threatening cardiac or metabolic crises.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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